1. Field of the Invention
The present invention generally relates to substrate inspection.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Transparent substrates such as silicon carbide and sapphire are frequently used in the fabrication of light emitting diodes (LEDs). Such transparent substrates are often polished on only a single side of the substrate. For example, the upper active surface is polished and the lower inactive surface remains unpolished. The upper active surface may also be patterned with voids or bumps.
It can be difficult to inspect the polished upper surface of the substrates described above and any transparent films formed thereon. For example, a light beam used by an inspection system will penetrate the transparent substrate and strike the bottom unpolished surface. Scattered light from the bottom unpolished surface can be collected and detected by the inspection system along with other scattered light that is desired to be detected. As a result, the scattered light signal from the unpolished bottom surface typically overwhelms the signal from the defects on the top surface and any transparent films formed thereon. In addition, in the case of a patterned substrate, the light will scatter from patterned structures formed on the upper active surface and that signal will be superimposed on the signal from the defects on the top surface and any transparent films formed thereon. Therefore, it can be difficult to detect any defects that might be present on the top surface of the substrate or in or on any transparent material formed thereon.
Accordingly, it would be advantageous to develop methods and systems for substrate inspection that do not have one or more of the disadvantages described above.